Boa constrictor is a species of large, heavy-bodied snake. It is a member of the family Boidae found in North, Central, and South America, as well as some islands in the Caribbean. Non-native boa constrictors, which can exceed 10 feet and 75 pounds, have established a breeding population in Puerto Rico, one that appears to be spreading, according to research published in the journal Biological Invasions. While boa constrictors and two species of pythons have established invasive populations in Florida, this research is the first to document a large constrictor species established in the United States or its territories outside of Florida. The new population appears to be spreading from its likely point of origin in the western part of the island around the city of Mayagüez. In the last year alone, more than 150 boas have been found in the wild on the island.

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Boa constrictor flourishes in a wide variety of environmental conditions, from tropical rainforests to arid semi-desert country. However, it prefers to live in rainforest due to the humidity and temperature, natural cover from predators and vast amount of potential prey. It is commonly found in or along rivers and streams. Prey includes a wide variety of mammals and birds. The bulk of their diet consists of rodents, but larger lizards and mammals as big as ocelots are also reported to have been consumed.

The established boa constrictor population likely originated from the pet trade. Genetic studies conducted by the researchers indicate that individual boas on the island are highly related and that the population probably originated with a small number of snakes that had been pets. First-hand accounts from local officials suggest that newborn boas were released in Mayagüez in the early 1990s.

"Experience has shown that island ecosystems are particularly vulnerable to snake invasions, and unfortunately Puerto Rico has no natural predators that can keep the numbers of these prolific, snakes in check," said USGS Director Marcia McNutt.

Two snakes found some distance from the expanding Mayagüez population share genetic markers with that population, suggesting that people might be intentionally or unintentionally moving the snakes around the island. Such movement could potentially increase the rate of spread of this invasive snake. Because the snakes are secretive and difficult to spot, the researchers suspect the population size is large.

"We’ve learned from dealing with other invasive snakes that understanding the source of these populations and preventing spread as soon as possible is important to protect ecosystems," said USGS scientist and study co-author Bob Reed.

Private ownership of boa constrictors and most other snake species is prohibited in Puerto Rico because of fears of non-native snakes becoming established. It did not seem to work.

It is not just in Puerto Rico. Breeding populations of Burmese python and boa constrictor have been confirmed in South Florida, and there is evidence that the northern African python is breeding in the wild as well. The reticulated python reaching and the green anaconda have both been found in South Florida.